1. Field of the Invention
This invention relates to a device for the measurement of the thickness of a blocked lens, and more particularly to a gauge suited for measuring the thickness of a lens supported on a block and using said thickness value to calculate other parameters of the lens.
2. Description of the Prior Art
In the manufacture of optical lenses such as eyeglasses or the like, it is necessary to produce the shape and dioptric power required by the prescriptions for the lenses. The accuracy of required properties so provided largely depends on the accuracy of measurements taken of the lenses during their laboratory processing. It is therefore necessary to provide means for accurately determining thickness and curvature of lenses. The task of accurately measuring lens parameters is complicated by the use of a lens holding block having variable thickness.
The prior art frequently utilizes templates against the workpiece for the determination of radius thereof. However, this requires the availability of a series of such templates and the matching process is slow and cumbersome since the fit of the template against the workpiece must be visually determined.
Spherometers and the device called Geneva Gauge are also used for measuring the radii of curvatures. The spherometers are used in conjunction with charts by which the sagitta measured is converted into radius of curvature or diopters. The Geneva Gauge, on the other hand, is calibrated to read directly in diopters. These devices are based on the same geometric principle. Namely, a device based on this principle has fixed contact points, usually steel balls, that are spaced apart twenty to fifty millimeters on the underside of the device. In use, these points contact the surface to be measured. Midway between the two fixed points is a plunger that moves up and down against spring tension on a line perpendicular to a line between the pair of fixed points. The up and down motion of the plunger rotates a pinion gear through a rack, integral with the plunger. On the same shaft with the pinion gear is an indicator needle capable of only two revolutions relative to the dial face, one revolution for convex curves and one for concave curves. The dial face is calibrated to read directly in diopters in increments of one-eighth diopter. The range of measurement is 17 diopters for both concave and convex curves.
Notwithstanding their advantages, the use of conventional mechanisms in these devices, such as racks, gears and other clock-work like components, results in a high failure rate. Such failure is most often caused by shock to the device, such as caused by sudden contact with other objects and personnel in the ophthalmic laboratory resulting in imprecise measurements or breakage.
It is therefore the principal object of the present invention to provide a simple, shockproof yet highly accurate device for measuring the blocked thickness of optical lenses.
It is another object of the present invention to utilize a rugged mechanism void of conventional components ordinarily used in lens measuring devices.
It is still another object of the invention to provide a device which directly shows the measured lens thickness and the dioptric power of the lens surface on a scale.
Other objects and advantages will be apparent from the description that follows.